Simulating Inner Radiation Belt Electron Transport and Low‐Latitude Precipitation Driven by Disturbance Electric Fields

Abstract

Increasing attention has been given to large‐scale disturbance electric fields in the inner radiation belt as a driver of drift‐periodic zebra stripe formations. Such disturbance electric fields have also been discussed as a possible driving mechanism of electron precipitation, transporting electrons below the inner belt and into the ionosphere‐thermosphere system. Here, we examine this mechanism during the 7–8 September 2017 geomagnetic storm using a combination of equatorial guiding‐center particle tracing simulations, Van Allen Probes particle measurements, and an adaptation of the Fejer and Scherliess (FS97) electric field model to drive radial transport. We find that our simulations capture the broad zebra‐stripe morphology of the observed radial transport, but require electric field amplitudes enhanced by a factor of 10 to reproduce the inferred transport magnitude, corresponding to electric field magnitudes of approximately −2.5 to 3.2 mV/m. Using an electric field model as a first approximation, we simulate the subsequent precipitation resulting from the transport, demonstrating that substantial electron fluxes can enter the low‐latitude ionosphere‐thermosphere system over timescales of a few hours following the electric field perturbation, spanning a wide range of equatorial longitudes. Unlike typical high‐latitude precipitation, the modeled particles approach the Earth along trajectories extended in longitude, shallow in angle to Earth's surface, implying broad longitudinally distributed energy deposition rather than localized, steep entry. These results demonstrate that disturbance electric fields can provide a rapid non‐diffusive pathway for transporting inner radiation belt electrons into the ionosphere‐thermosphere system, and a mechanism that is not well represented in current radiation belt or atmospheric models.